True. What I meant was that the dialogue should add to the story in some way. As someone else pointed out you shouldn't go into a long spiel about what's for dinner unless it has some bearing on the story itself. For example if it's a story where the husband's boss is coming to dinner and he's allergic to something or if she's trying to impress her new mother-in-law etc. Dialogue has text and subtext. The text tells us direct information and the way it's presented tells us about the characters who are speaking the dialogue.

Yep, this is all true ... to an extent. But there is still a lot that happens in most books that has questionable reason to be there, dialogue and other. Besides the obvious stuff, character and scene building and so on, there can be less obvious reasons for text and dialogue:

A scene needs some continuity - to avoid that jerky feeling you get of a movie that jumps from scene to scene before you've even had a chance to grasp what's going on. But you also have to trust the reader to a certain extent, knowing that they will fill in some gaps for themselves - and finding the right compromise between the two is neither easy nor obvious (at least, not to me).

Many (most? all?) stories have an element of mystery, and you want to feed into that mystery with both your text and your dialogue. If every word that every character speaks is dripping with meaning then you risk spoiling that mystery. Sometimes words are used to hide other words. When the mystery is finally revealed you want the reader to realise that it all makes sense, that they could have seen this coming if only they'd known which words were important. But the author has to decide how much is enough - or too much.

If I've been clear, then you can see that I'm not really disagreeing. Yes, every part of a book, dialogue and text, should have a reason to be there. But such a simple statement of the rule hides the complexity, and the subjectivity, that really exists. I can pick up almost any book that I've read in the past and immediately pick out phrases that could be deleted as not essential, that could be deleted with no real impact on the story, but if all such phrases were deleted the book is likely to become a shell of its former self. It wouldn't read or feel the same any more (and sometimes that might be a good thing ).

Sometimes the dialogue while sitting down to dinner is painting the scene in which something more important is about to happen. The dialogue itself could be removed, or replaced with "They sat down to dinner and talked," but such a simplification may remove the tone of the setting that you wanted for the important event.

The words we use are like brush strokes on a painting, some are there only to support the ones that need to stand out. Use too much background and you will obscure the impact or meaning of the highlights, use to little and the painting becomes all highlights and its purpose is lost.

Just remember ALL of it can be ignored or followed religiously or anything in between. There are no RULES in writing only SUGGESTIONS.

Also no matter what stance you take... many will tell you that you are wrong.

Yep. No rule of writing applies in all situations. The rules for writing an essay for example are different than those for writing a short story. And there are different sets of 'rules' for different genre's of fiction as well. For example you don't find too many mysteries where a love story is the main event. Two characters in a mystery may fall in love during the course of solving the mystery, but it's the mystery that is at the center of things, not the romance. Also people redefine what fits in a genre on occasion creating sub genre's of a particular genre. For that matter you can't say that there is only one way to write a story either. Some people create in-depth outlines before they write one word and some just sit down and start writing. What works for one might not work for another.